A hydrotreating catalyst may be defined as any catalyst composition which may be used to catalyze the hydrogenation of hydrocarbon feedstocks to increase its hydrogen content and/or remove heteroatom contaminants. A hydrocracking catalyst may be defined as any catalyst composition which may be used to catalyze the addition of hydrogen to large or complex hydrocarbon molecules as well as the cracking of the molecules to obtain smaller, lower molecular weight molecules. A residuum hydroconversion process may be defined as a process for converting petroleum atmospheric or vacuum residue at conditions of elevated temperatures and pressures in the presence of hydrogen and a hydrotreating and/or hydrocracking catalyst to convert the feedstock to lower molecular weight products with reduced contaminant (such as sulfur and nitrogen) levels.
Catalyst compositions for use in the residuum hydroconversion process are well known to those skilled in the art and several are commercially available. Suitable catalysts include catalysts containing nickel, cobalt, tungsten, molybdenum and combinations thereof supported on a porous substrate such as silica, alumina, titania, or combinations thereof.
For maximum effectiveness these metal oxide catalysts are converted at least in part to metal sulfides. The metal oxide catalysts can be sulfided in the reactor by contact at elevated temperatures with hydrogen sulfide or a sulfur-containing oil or feedstock.
The catalysts may also be provided to the end-user already having sulfur incorporated therein. However, these ex-situ methods of presulfurizing supported metal oxide catalysts have suffered from excessive stripping of sulfur upon start-up of a hydrotreating reactor in the presence of a hydrocarbon feedstock. As a result of sulfur stripping, a decrease in catalyst activity is observed. It is therefore well known in the art that the activity and activity maintenance of the above mentioned metal oxide catalysts is substantially enhanced by presulfiding of the catalysts in the manufacturing process or in-situ during startup of the hydroconversion process.
Hydroconversion processes can operate in a fixed catalyst bed mode in which a batch of catalyst is utilized in the hydroconversion reactors for periods of typically three months to twenty-four months before the process is shut down to remove and replace the catalyst. In this fixed-bed mode, catalyst can be presulfided during unit startup to achieve maximum levels of catalytic performance (hydrogenation, desulfurization, denitrogenation, conversion, etc.)
In hydrotreating/hydrocracking processes, which add and withdraw catalyst on a regular basis (i.e. daily, weekly) while the process operates at normal conditions of temperature and pressure, catalyst is typically added in an as-manufactured state (i.e. containing metal oxides). Processes which operate in this mode include ebullated-bed hydrocrackers (such as H-Oil.TM. Process), moving-bed hydrotreater, Onstream Catalyst Replacement reactors (OCR) and guard reactors used in fixed-bed resid hydrotreaters.
In ebullated-bed processing applications, which utilize first generation low activity catalysts, minimal advantage has been identified for presulfiding the catalysts to be added on a daily basis. These catalysts achieve some presulfiding upon addition to the hydroconversion reactor. However, such operations that utilize new second and third generation catalysts (high desulfurization, low sediment), a significant increase in desulfurization, denitrogenation, and Conradson carbon removal can be achieved by presulfiding the catalyst additions.
The benefits of catalyst presulfiding in general are well known in the prior art. For example, the use of high boiling oils, such as vacuum gas oils, and hydrocarbon solvents to aid the incorporation of sulfur into a catalyst is taught in U.S. Pat. No. 4,943,547, issued Jul. 24, 1990. Further, U.S. Pat. No. 4,530,917, issued Jul. 23, 1985, to Berrebi discloses a method of presulfurizing a hydrotreating catalyst with organic polysulfides.
U.S. Pat. No. 4,117,136, issued Dec. 4, 1979, to Herrington et al discloses a method of catalyst presulfurizing wherein a catalyst is treated with elemental sulfur. Hydrogen is then used as a reducing agent to convert the elemental sulfur to hydrogen sulfide in situ. U.S. Pat. No. 4,089,930, issued May 16, 1978, to Kittrell et al discloses the pretreatment of a catalyst with elemental sulfur in the presence of hydrogen. All of the aforementioned patents are hereby incorporated by reference into this application.
This invention describes an improved method for achieving the catalyst presulfiding and preconditioning during normal plant operations but prior to addition of the catalyst to the catalytic reactor and can be accomplished in most situations with minimal equipment changes. This provides the benefit of being able to retrofit existing units as well as implementing on grass roots applications. Moreover, the invention allows for the preconditioning of the residuum hydrotreating or hydrocracking catalyst without interrupting the continuous operation of the resid hydroconversion process. Importantly, the resid hydroconversion process of this invention can operate continuously for several years while maintaining high catalyst activity.